Lactobacillus casei is propagated under essentially anaerobic conditions to provide a starter culture for manufacture of Swiss cheese. The culture produces lactic acid as a by-product of energy metabolism. The system has the following characteristics: YXS=0.23kgkg1KS=0.15kgm3max=0.35h1mS=0.135kgkg1h1 A stirred fermenter is operated in fed-batch mode under quasi-steady-state conditions with a feed flow rate of 4m3h1 and feed substrate concentration of 80kgm3. After 6h, the liquid volume is 40m3. 1. What is the initial culture volume